Effect of Closing Date on Dry Matter Yield and Leaf Proportion in Perennial Ryegrass Swards During the Early Winter Period08 January 2013
Perennial ryegrass is a common dairy pasture species in Ireland which has been tested for responses to closing dates at the grazing seasons's end by researchers at Teagasc.
Herbage growth in Ireland is highly seasonal with peak growth rates in summer and little or no growth in winter (Brereton, 1995). During the winter period, growth of perennial ryegrass (PRG; Lolium perenne L.) is characterised by a reduction in leaf extension rate and an increase in leaf senescence rate (Hennessy et al 2008). It is common to feed livestock indoors with conserved forage and concentrate for the winter period. One alternative is to accumulate grass so that it can be grazed in situ thereby extending the grazing season into the autumn/winter period. The objective of this study was to investigate the effect of closing date on herbage mass (HM), sward morphology, sward chemical composition and PRG population (sward density) throughout the early winter period (October-November).
Materials and Methods
A one year old PRG sward (79% PRG) at Teagasc Moorepark, Fermoy, Co. Cork, which was previously
grazed, was divided into 24 (3 x 5 m) plots. The study was a randomised block design with 2 x 4 factorial
arrangement of treatments, replicated three times.
Two closing dates (CLD: 8 August (E) and 15 September (L), 2011) were defoliated on four harvesting dates (HD: 3 October (HD1), 17 October (HD2), 31 October (HD3) and 14 November (HD4)). In total, the sward received 230 kg fertiliser nitrogen during the year.
Plots were harvested with an Etesia rotary blade mower to a stubble height of 4 cm across all treatments. The herbage removed from each plot was weighed and sampled to determine HM. A 100 g sub-sample was dried for 48 h at 40ºC to measure the dry matter (DM) content of the sample and calculate the DM yield/ha.
The dried sample was then milled and analysed for dry matter digestibility (DMD) and crude protein using near infra-red spectrometry (NIRS). Prior to harvesting, tillers were sampled by cutting to ground level using a scissors and a 40 g subsample was separated into leaf, stem and dead components above and below a 4 cm stubble height. Also, three 10 cm2 turves were taken from each plot.
The tillers of PRG, weed grass and broad leaf weeds were counted on each sod sample to assess sward density and PRG proportion. Data were analysed using PROC MIXED in SAS 2006, CLD, HD, CLD*HD and replicate were included in the model.
The Interaction of Closing and Harvesting Dates on DM Yield and Leaf Proportion
The earlier closing date resulted in higher overall herbage mass accumulation. As DM yield increased there was a decline in leaf proportion above a 4 cm stubble height and in PRG tiller density. Hence, as grazing date moves later into the season, herbage quality will decrease, in terms of leaf proportion and (DMD). Further investigation is required, but this study shows that swards reach a maximum DM yield during autumn irrespective of rotation length.
Brereton, J. (1995). Irish grasslands their biology and management (ed. D. W. Jeffrey, B. M. Jones and J. H.
Hennessy, D., O’Donovan, M., French, P., Laidlaw A.S. (2008). Grass and Forage Science, 63:202-2 SAS, (2006). SAS Institute. Cary, NC, USA.